1. Field of the Invention
The present invention relates to an optical system, and more particularly, to an optical system configured of 4-sheet lenses to have a wide angle of view by being mounted on mobile communications terminals, PDAs, or the like, or used in a monitoring camera and a digital camera, or the like.
2. Description of the Related Art
Recently, research into a camera module for a communications terminal in connection with an optical system, a digital still camera (DSC), a camcoder, a PC camera (an optical device attached to a personal computer), or the like, has been conducted. In the image pickup system, the most important component, in order to obtain images, is a lens system forming images, that is, an optical system.
Since the optical system requires high performance in terms of resolution, quality of image, and the like, the configuration of the lens is complicated. The size of the optical system is increased when the optical system is structurally or optically complicated, such that there is a problem in realizing compactness and slimness in the optical system.
For example, in order to increase the mounting effectiveness of a camera module mounted on a mobile phone, the compactness of the entire module is an indispensable condition. In addition, in an image sensor of a CCD or a CMOS used therefor, resolution is gradually being increased and the size of the pixels is gradually being reduced. The lens system corresponding thereto is therefore required to have slimness and compactness as well as being able to satisfy the requirements for high resolution and excellent optical performance, and the like.
In this case, when a 3-megapixel optical device (CCD or CMOS) is used, optical performance and compactness can be satisfied even in the case that lenses configuration of 3 sheets or less are used; however, in the case that lenses of 3 sheets or less are used in a high-resolution optical device (CCD or CMOS) of 5-megapixels or more, the refractive powers of each lens are large and thus, the lenses cannot be easily processed, such that it is difficult to simultaneously satisfy the requirements of high performance and compactness. In addition, despite having a lens configuration of 4 sheets or more, the entire length of an optical system is increased when a spherical lens is used, such that it is difficult manufacture to have a small size. In addition, an optical system having a 4-sheet lens configuration can secure good optical characteristics when it is generally designed to have an angle of view of 55 to 68°; however, a degradation in yield due to the increase in sensitivity is caused when it is designed to have the angle of view of 68° or more.
Therefore, in an optical system having a 4-sheet lens configuration, a need exists for a technology capable of simultaneously implementing compactness, high optical performance, and a wide angle of view.